JP2000121574A - Flaw inspection apparatus for steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flaw inspection apparatus for a steel plate, by which all kinds of flaws can be detected with a simple constitution and without being restricted by an installation place. SOLUTION: A linear light source 12 which shines radiates the surface of a steel plate 1 with illumination light is installed obliquely by setting an angle θto the horizontal direction with reference to a line C which is at a right angle to a line direction. A camera 14, which pickes up its reflected light images, uses the nearly whole width on the surface of the steel plate as the visual field of an image pickup operation, and the angle of elevation from the center of the visual field is set according to the arrangement state of the linear light source 12. Thereby, the linear light source 12 can irradiate with the illumination light so as to form a shadow in the reflected light image in the same manner as an uneven flaw, and a linear flaw in the line direction can be detected surely.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flaw inspection apparatus for a steel sheet, and more particularly to a flaw inspection apparatus for a steel sheet which inspects various flaws on the surface of a steel sheet such as a coated steel sheet using photographed images.

[0002]

2. Description of the Related Art Among steel sheets and the like, quality inspection of shipment is important for painted steel sheets and the like which are used as they are in a case of a product in a form that can be seen by users and consumers after shipment.
The flaws which become a problem in the coated steel sheet include (a) change in color tone (garbage spots, unevenness, gloss unevenness, etc.), and
(C) L (line) direction linear flaws (flaws in the plate flow direction such as linear cissing and flaws). Inspection of such flaws is required to be performed in a non-contact manner while continuing to transport the coated steel sheet, and it is required to be able to detect slight differences in color tone and unevenness and linear flaws in the transport direction. .

Conventionally, inspection of surface flaws on steel sheets and the like has been disclosed in, for example, Japanese Patent Application Laid-Open No. 7-218451.
In many cases, a plurality of illuminations and cameras are arranged for each type of flaw, and the illumination photographing direction is set to be perpendicular or parallel to the transport direction of the steel plate.

FIG. 4 shows a conventional example of an apparatus for inspecting a flaw of a steel sheet such as a painted steel sheet. Above the steel plate 1, two cameras 2 and 3 are installed at predetermined intervals in the direction in which the steel plate 1 is conveyed.
Furthermore, in front of the cameras 2 and 3 (with respect to the transport direction of the steel plate 1)
Are provided with light sources 4 and 5 at a predetermined height. The light source 4 is disposed such that the emitted light 6 is reflected on the surface of the steel plate 1 and the reflected light 7 is incident on the camera 2. Similarly, the light source 5 is disposed such that the emitted light 8 is reflected on the surface of the steel plate 1 and the reflected light 9 is incident on the camera 3. The incident angle of the light 6 on the steel plate 1 is set to a larger value than the light 8. That is, irradiating from a high position like the light source 4 makes it easier to detect a color tone change flaw, and irradiating from a low position like the light source 5 makes it easier to detect an uneven change flaw. As a result, light with different irradiation directions can be projected according to the state of the flaw, so that various flaws can be detected in combination with two cameras. In FIG. 4, the light source and the camera are arranged on a flat portion of the steel plate because they are schematically shown. However, in actuality, a feed roller (not shown) is used to secure the smoothness of the steel plate 1 and to prevent vibration. It is arranged near.

In the configuration shown in FIG. 4, when the steel sheet 1 is conveyed in the direction A in the figure, the light 6 of the light source 4 is reflected on the surface of the steel sheet 1 and enters the camera 2, and the light 6 of the light source 5 is also transmitted. Is reflected on the surface of the camera and enters the camera 3. When there is a flaw on the reflective surface,
A contrast corresponding to the flaw shape is generated, and one flaw image is formed. Since the camera 2 and 3 have different light irradiation angles, the flaw images are captured as flaw images of different shapes. Image signals output from the cameras 2 and 3 are processed by a processing device (not shown), and the presence / absence of each type of flaw is determined. When the steel plate 1 is coated on both sides, a flaw inspection is also performed on the back surface.

[0006]

However, the above conventional example has the following problems. (1) In some cases, linear flaws are difficult to detect or cannot be detected. Although shadows can be formed by selecting the angle of incidence of the illumination light, smoothness was not obtained due to the effect of the tension applied to the steel plate, and the reflected image was distorted and could not be detected. (2) The installation location of the flaw inspection device is limited to the roller wrapping portion from the viewpoint of ensuring smoothness and considering vibration. Further, in order to prevent the camera from being out of focus, equipment costs are increased, and time is required for adjustment work. (3) Two light sources and two cameras are required for flaw inspection, and time is required for adjustment on site. (4) Since two light sources and two cameras are required, equipment costs increase.

[0007] In order to solve the above problems, an object of the present invention is to provide a flaw inspection apparatus for a steel sheet which can detect all kinds of flaws with a simple configuration and without being restricted by an installation place. It is in.

[0008]

In order to achieve the above object, the invention according to claim 1 of the present application illuminates the surface of a steel sheet with illumination light, images the reflected light, and images the surface of the steel sheet. In a flaw inspection device for steel plates for inspecting various flaws, a reflector is disposed obliquely at a predetermined angle with respect to the transport direction of the steel plate, and covers almost the entire width of the surface of the steel plate to prevent direct light incidence of illumination. And a light source that illuminates a wide and reflected light parallel to the steel plate, and a field of view covers substantially the entire width of the surface of the steel plate illuminated by the light source, and the elevation angle from the center of the field of view depends on the arrangement state of the light source. A flaw inspection device for a steel plate, comprising: a camera set in advance.

According to this structure, the light source for illuminating in the width direction of the plate is arranged obliquely, not perpendicular to the line direction of the steel plate, so that the illuminating light is not parallel to the line width direction but extends in the line direction. Irradiation is performed on the flaws in an oblique direction, and a shadow is formed in the reflected light image from the linear flaws. Further, even if the reflected light is distorted due to the tension of the steel sheet, by providing a wide light source, it is possible to provide a uniform luminous intensity over the entire inspection width.
Further, by setting the installation position of the camera in accordance with the arrangement of the light source, the camera captures a clear image.
Therefore, linear flaws in the line direction and other kinds of flaws can be reliably detected with a simple configuration.

[0010] The invention according to claim 2 of the present application is the apparatus for inspecting flaws on a steel sheet according to claim 1, wherein the predetermined angle is less than 90 degrees.

According to this configuration, it is possible to form a shadow optimal for imaging by a camera with respect to the light image reflected from the linear flaw with a simple configuration, and it becomes easy to detect the linear flaw.

According to a third aspect of the present invention, there is provided the steel plate flaw inspection apparatus according to the first aspect, wherein the elevation angle is less than 90 degrees.

According to this configuration, it is possible to capture an image of a reflected light in which a linear flaw is formed by a light source arranged obliquely, without impairing the state of the shadow.

According to a fourth aspect of the present invention, there is provided the steel plate flaw inspection apparatus according to the first aspect, wherein the luminous body of the light source is a linear light source.

According to this configuration, it is possible to obtain a linear light source such as a fluorescent lamp that illuminates the entire width of the steel plate with one light source.

According to a fifth aspect of the present invention, there is provided the steel plate flaw inspection apparatus according to the first aspect, wherein a reflection plate for preventing light from directly entering the camera is provided. .

According to this configuration, it is possible to give only the intended reflected light to the camera.

The invention according to claim 6 of the present application is the steel sheet inspection apparatus according to claim 1, wherein the light source applied to the steel sheet is a parallel light beam and is broad and uniform. .

According to this configuration, even when the reflected image is bent due to the distortion of the steel plate when the light is obliquely irradiated, the entire inspection width can be reduced.
A uniform light intensity can be provided.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a steel sheet flaw inspection apparatus according to a first embodiment of the present invention. The flaw inspection device according to the present invention
The apparatus includes a linear light source 12, such as a fluorescent lamp, a camera 13, and a processing device 14. The processing device 14 includes a storage device that stores the processing result, a display device that displays the processing result, and a recording device such as a printer. Feed roller 1
0 and the take-up roller 11 are installed at a predetermined distance, and the steel sheet 1 drawn from the feed roller 10 is taken up by the take-up roller 11 while being conveyed in the B direction.
A flat surface is formed between the feed roller 10 and the take-up roller 11. Above this flat surface, a single linear light source 12 and a camera 13 constituting the flaw inspection device are installed.

The linear light source 12 is desirably a linear light source because it needs to illuminate the wide steel plate 1. Therefore, the linear light source 1
For example, a fluorescent lamp 12a (a high-frequency fluorescent lamp, a high-intensity fluorescent lamp, or the like) is used as the second light emitter. Then, the light from the linear light source 12 is prevented from directly entering the camera 13, the illuminance on the steel plate 1 is increased, and a wide reflected light can be emitted.
A semicircular reflector 12b is provided above the fluorescent lamp 12a. A camera using a CCD image sensor is suitable for the camera 13 because it can be reduced in size and weight. A processing device 14 is connected to the camera 13, and the presence or absence of a flaw, the size of the flaw, and the like are determined.

FIG. 2 shows the arrangement of the linear light source 12 and the camera 13 viewed from above, and FIG. 3 shows the linear light source 1 viewed from the front.
2 and the arrangement status of the camera 13 are shown. As shown in FIG.
The linear light source 12 is disposed obliquely at an angle θ in the horizontal direction with respect to a line C perpendicular to the plate width direction, and as shown in FIG. Same to you. By arranging the linear light source 12 obliquely,
Since the incident light with respect to the linear flaw extending in the line direction is obliquely irradiated, the reflected image can be shaded, and the linear flaw can be reliably detected. The angle θ is 90
The closer it is to the degree, the more shadows can be added, but the inspection width is widened and the resolution is reduced. Further, the distortion of the reflected image increases, and it becomes difficult to secure a wide and uniform light source. Therefore, for practical use, the angle θ should be 2
When the angle was set to 0 degree or more, a result was obtained in which a shadow capable of detecting a linear flaw could be formed.

As shown in FIG. 2, corresponding to the oblique arrangement of the linear light source 12, the camera 13 is moved to a position at a distance at which a viewing angle α is obtained at which the entire width just below the center line D of the linear light source 12 can be photographed. Has been installed. At this time, the reflected light E of the illumination appears slightly distorted like a gentle wave on the steel plate. However, since the illumination is wide and uniform, the entire inspection width can be photographed with uniform luminous intensity. Further, regarding the installation of the camera 13, as shown in FIG. 1 and FIG.
The elevation angle β of the camera 13 as viewed from the center of the visual field (the center of the range illuminated by the linear light source 12 on the steel plate 1) is defined so that the direction linear flaw can be detected well. Linear light source 1
When 2 was set to 20 degrees, and when the elevation angle β was 59 degrees, the best results could be obtained in which any of color tone flaws, uneven flaws, and linear flaws could be detected.

The image output from the camera 13 is input to a processing device 14, which performs processing for flaw determination. First, data integration is performed on the image output of the camera 13, and a difference process is performed based on the integrated value. From the change in the difference value, the presence or absence of a flaw, the degree of the flaw, and the like can be known. The difference value can be obtained as [several integrated values before and after including target data] − [several right integrated values not including target data]. By calculating this difference value N (for example, 5,000) in the plate width direction,
In addition to grasping the whole image, it is possible to efficiently detect only the target flaw information by suppressing common environmental change factors such as vibration influence and illuminance change, dust of the lens, and deterioration of the performance of the detector.

As described above, according to the embodiment of the present invention, it is possible to detect a linear flaw, which has been conventionally difficult, with a simple configuration using one linear light source and one camera. It should be noted that other types of flaws such as irregularity change flaws can form a shadow even when illuminated from any direction,
Flaw detection can be performed without any problem. Further, since the flaw inspection device may be installed anywhere between the rollers, the maintenance inspection is easy without being restricted by the installation location.

[0027]

Examples are shown in Table 1. Using this method, other types of flaws, including linear flaws, can be reliably detected with a simple configuration.

[0028]

[Table 1]

[0029]

As described above, according to the first aspect of the present invention, the surface of the steel sheet is irradiated with illumination light, and the reflected light is imaged to remove various flaws on the surface of the steel sheet. In the flaw inspection device for a steel plate to be inspected, a light source for illuminating the width direction of the steel plate is disposed obliquely with respect to a line perpendicular to the width of the steel plate, and from a center of a field of view of a camera that captures a reflection image from the steel plate. Since the elevation angle is set optimally, the illumination light is applied obliquely to the linear flaws extending in the line direction, and a shadow can be formed on the reflected light image from the linear flaws. Linear flaws and other types of flaws can be reliably detected.

According to the invention of claim 2 of the present application, since the mounting angle of the light source is set to less than 90 degrees, it is possible to form a shadow optimal for image pickup by a camera on a light image reflected from a linear flaw. And detection of linear flaws becomes easy.

According to the third aspect of the present invention, since the elevation angle with respect to the camera is set to less than 90 degrees, a reflected light image having a shadow formed by a light source arranged obliquely can be used.
An image can be taken without impairing the shadow state.

According to the invention of claim 4 of the present application, since the luminous body of the light source is a linear light source, a linear light source that illuminates the entire width of the steel plate with one light source can be obtained.

According to the invention of claim 5 of the present application, it is possible to give only the intended reflected light to the camera.

According to the invention of claim 6 of the present application, when the oblique irradiation is performed, even if the reflection image is bent due to the distortion of the steel sheet,
A uniform luminous intensity can be given over the entire inspection width.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing a steel sheet flaw inspection apparatus as a first embodiment of the present invention.

FIG. 2 is a plan view showing the arrangement of a light source and a camera as viewed from above in FIG. 1;

FIG. 3 is a front view showing an arrangement state of a light source and a camera as viewed from the front in FIG. 1;

FIG. 4 is a schematic front view showing a conventional configuration of a steel plate flaw inspection apparatus.

[Explanation of symbols]

 Reference Signs List 1 steel plate 2 camera 3 camera 4 light source 5 light source 6 light 7 reflected light 8 light 9 reflected light 10 feed roller 11 take-up roller 12 linear light source 12a fluorescent lamp 12b reflector 13 camera 14 processing device θ angle α viewing angle β elevation angle

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Toshimichi Murata, 1 Kimitsu, Kimitsu, Nippon Steel Corporation Inside of Kimitsu Works (72) Inventor, Sonori Nagase 1 Kimitsu, Kimitsu, Nippon Steel Corporation Kimitsu Works (72) Inventor Ryoji Nishioka 1 Kimitsu, Kimitsu City Nippon Steel Corporation Kimitsu Works (72) Inventor Yoshiro Yamada 5-26-12 Minamioi, Shinagawa-ku, Tokyo Technos Co., Ltd. F term (reference) 2G051 AA37 AB01 AB07 BB01 CA03 CA04 CB01 EA16

Claims (6)

[Claims] 1. A steel sheet flaw inspection apparatus for irradiating illumination light onto a surface of a steel sheet and imaging reflected light thereof to inspect various types of flaws on the surface of the steel sheet. A light source that is arranged at a predetermined angle and illuminates substantially the entire width of the surface of the steel sheet, and has a field of view that covers substantially the entire width of the surface of the steel sheet illuminated by the light source, and the elevation angle from the center of the field of view is the elevation angle. A flaw inspection device for a steel plate, comprising: a camera set according to an arrangement state of a light source. 2. The apparatus according to claim 1, wherein the predetermined angle is less than 90 degrees. 3. The apparatus according to claim 1, wherein the elevation angle is less than 90 degrees. 4. The apparatus according to claim 1, wherein the light source is a linear light source. 5. The apparatus according to claim 1, wherein the light source is provided with a reflector for preventing light from directly entering the camera. 6. The apparatus for inspecting flaws on a steel sheet according to claim 1, wherein the light source has a wide and uniform width of the parallel light irradiated and reflected on the steel sheet.